The present invention relates to a material sortation system and more particularly to a sortation system of the type comprising of a plurality of transport units, and movable on a track. Items to be sorted are loaded onto the transport units and are unloaded at specified addresses or destination ports along the track
In a known material sortation system, each of the transport units comprises a tray which is connected to a tray tilting mechanism. The tray tilting mechanism allows the tray to be tilted to one side, but more usually to both sides, of the direction of travel of the tilt tray units in the track. In this way items loaded onto the trays can be discharged into selected destination ports
In a further known material sortation system, each of the transport units comprises a small conveyor or xe2x80x98cross beltxe2x80x99. The conveyor allows items, which are loaded upon it, to be propelled to either side of the direction of travel of the transport units along the track. In this way items loaded onto the conveyors can be discharged into selected destination ports.
Tilt tray and cross belt sorters are well known for their ability to handle a wide variety of products at large throughput rates and high speed with great accuracy. Tilt tray sorters are generally used in luggage handling systems at airports, central distribution warehouses, and parcel handling installations. Cross belts are more commonly used for the sortation of smaller items where the width of the destination port is narrow. The cross belt sorter powers the items into the chute whereas the tilt tray sorter allows product to drop into a destination port under the effect of gravity. As a consequence the width of the destination port can be made narrower for a cross belt sorter.
Tilt tray sorters are in the main mechanically operated, although electrically powered tilt tray units are known.
While an electrically powered tilt tray unit offers many advantages over a mechanical tilt tray unit, there are still some limitations to existing designs. A transmitter must be placed at each tip position along the track to initiate tilting and must be identified to control software within the sorter control system. Anytime a tip position is changed, the transmitter associated with it must be repositioned and changes in the control software need to be made. Furthermore there is considerable installation cost to install tip transmitters in terms of electrical site wiring, software and commissioning.
As a transmitter must be situated immediately adjacent to each tip position, a number of transmitters are required to produce a good fill pattern for wide chutes. Although it is relatively easy to install several transmitters for an electrically powered tilt tray unit, these transmitters all require wiring, software control, installation and commissioning time. There is also a limit on the number of tip positions for a single chute due to the physical size of the transmitters, their mounting brackets and associated wiring.
Once programmed the tip profile of the trays can not be readily changed. Yet it would be beneficial to be able to selectively vary the tray tip profile, for example, to tip a tilt tray more vigorously when luggage became wet, and to tip it gently when fragile items are carried.
One limitation of the throughput of a tilt tray sorter is the sorter speed. The number of items which can be sorted can be no greater than the number of trays passing the sorter loading area in a given time. Yet there is a maximum speed at which trays can safely travel along the track and above this speed there is always the risk that items on the trays will be flung off when the tray travels around bends in the track.
An electrically powered tilt tray sorter is also required to communicate with the sorter control system at specific locations around the sorter track. When the sorter stops the electrical power to the tilt tray units is switched off for safety reasons. When the sorter restarts all of the tilt tray units then need to be reset so that they will respond to tip commands. This function is performed at a certain position by means of a transmitter, which is activated as the tilt tray unit passes over it. Similarly when a tilt tray unit has had a fault, and is in the fault condition, the tilt tray unit is reset in this way.
The tilt tray units once reset, switch on an on board transmitter which signals to the sorter control system that it is ready to receive items. If a tilt tray unit develops a fault the on board transmitter is switched off. The status of the tilt tray units is read at set positions by an in track receiver.
Due to the fact that the transmitters and receivers are read at a limited number of set positions, inherent delays may occur on sorter start up as all of the tilt tray units need to pass the reset position before items can be loaded onto the trays and before tip commands can be passed to individual tilt tray units. If a fault condition occurs a tilt tray unit can not communicate the type of fault, only that a fault has occurred due to the fact that the on-board transmitter provided with it only allows an on or off signal.
For ease of understanding a typical electrically powered tilt tray sorter will now be described with reference to FIGS. 1 and 2 of the accompanying drawings.
Referring firstly to FIG. 2 there is shown two electrically powered tilt tray units 101 and 102 which are linked together to form a continuous train. Each tilt tray unit comprises in the lower part thereof an aluminium box section 2 which surrounds a steel plate 1. The steel plate 1 forms a reaction plate for a linear induction motor. These linear induction motors serve to drive the continuous train around a track (not shown). The speed of the continuous train around the track is determined by sensor means (not shown) on or adjacent to the track which is able to detect the marks on an encoder strip 3 which runs along the side of each box section 2 and a central control then uses this to regulate the speed of the continuous train around the track.
Referring now to FIG. 1, each tilt tray unit comprises a braked electric motor 4 which is connected at each end thereof to a pair of arms 5 which in turn support a tray 103, shown only in FIG. 1 for ease of illusion. The motor 4 is operable to rotate the tray 103 backwards and forwards about its drive axis, thereby allowing items on the tray 103 to be discharged from it. The tray 103 is normally held in the horizontal position, as shown in FIG. 1, by the braked motor 4.
Each tilt tray unit comprises at the forward end thereof a horizontally extending support bar 104 which carries at each end a roller assembly 105 and 106. The roller assemblies 105 and 106 are each engageable in a respective channel defined by the aforementioned track. The operation of each tilt tray unit is controlled by receiver and transmitter devices carried by the unit itself and at predetermined locations around the track, as will now be explained.
Each tilt tray unit is reset after a fault condition or the loss of power by the operation of a tray reset transmitter mounted in the track. As a tilt tray unit passes over the reset transmitter, the transmitter is switched on, and a reset receiver (not shown) on the unit itself picks up the signal. The reset receiver outputs a signal to a controller 11 mounted on the tilt tray unit, which controller 11 effects a reset and enables the tilt tray unit. When the tilt tray unit is thus enabled a unit enabled transmitter 9, carried on the horizontal support bar 104, is switched on and remains switched on until a fault occurs or the power to the tilt tray unit is switched off.
Also located in the track is a unit enabled receiver which is able to detect the output from each unit enabled transmitter 9. As each tilt tray unit passes over the unit enabled receiver the status of it""s transmitter is detected or xe2x80x9creadxe2x80x9d and in this way the status of each unit is determined. Those tilt tray units which are determined to be disabled are taken out of service such that no further items are loaded onto the trays thereof.
Also located in the track at predetermined locations along its length are pairs of tilt tray unit tip transmitters. The outputs from these transmitters are sensed by each tilt tray unit through the medium of a pair of receivers 7 and 8 carried at one end of the horizontal support bar 104. It will be understood that depending on the signals output from each pair of transmitters the tray of each tilt tray unit, as it passes the transmitters is caused to tip or remain level. More specifically, if the receiver 7 detects a signal the controller 11 operates the motor 4 to cause the tray to tip right, if the receiver 8 detects a signal the tray is tipped left, and if both receiver 7 and 8 detect a signal simultaneously the tray is maintained level.
Once the controller 11 sees the output from the receivers 7, 8 and 9 a tip, straighten or reset sequence is initiated for the tilt tray unit. The tilt tray unit will always reset as long as a failsafe limit switch contact 15 is made by the action of a position flag 16 as the tray rotates. The limit switch 15 is used to trip the controller 11 if the tray has tipped past its maximum angle of rotation. The controller 11 defines the tip and straighten sequences. The program in the controller 11 defines rotational speed of tip and uses three sensors 17, 18 and 19 to provide positional feedback in order to control the angle of tip, and the horizontal position of the tray as it is straightened.
It is an object of the present invention to provide a tilt tray sortation system which provides simpler and more effective means for communicating with and controlling the operation of each transport unit over the known system referred to hereinabove.
According to the present invention there is provided a sortation system comprising a plurality of transport units connected end to end to form a continuous train and mounted for movement along a track defining at intervals along its length destination ports at which items carried by the transport units may be discharged under the control of a central control system, wherein the central control system comprises a radio frequency transmitter device through which control signals to the continuous train are transmitted and the continuous train comprises a radio frequency receiver device for receiving the transmitted control signals.
Preferably, the radio frequency transmitter device is connected to a leaky feed aerial which extends the length of the track. The leaky feed aerial may comprise a screened cable having holes in the screening at intervals along its length. The leaky feed aerial may run parallel to the track. Alternatively, it may run within the track itself.
The use of a leaky feed aerial to transmit control signals from the central control system to the continuous train ensures that there are no dead or null spots around the track. In this regard, the track, the destination ports and any associated apparatus can shield and otherwise obstruct the signal from a simple omnidirectional aerial.
Each of the transport units may comprise a radio frequency receiver device connected to an on-board local controller which operates a discharge mechanism of the transport unit in response to received control signals. However, in a preferred embodiment of the present invention the continuous train comprises at least one master transport unit and a plurality of slave transport units associated with the or each master transport unit, and the or each master transport unit comprises a radio frequency receiver device connected to an on-board local controller which operates the discharge mechanism of the master transport unit and each of the slave transport units associated therewith in response to received control signals.
In order to ensure that items carried by a particular transport unit are discharged to the correct destination port, the sortation system in accordance with the present invention further comprises means for determining the position of each transport unit relative to a fixed datum position on the track. In this regard, the position determining means comprises means for detecting the passage of a designated transport unit past a fixed datum position on the track, a counter and means for initiating the distance determining means on detection of the said designated transport unit. The distance determining means may comprise a wheel which turns against the continuous train, or encoder markings running the length of the track which are detectable by optical means. Preferably, the distance determining means comprises sensor means mounted in the track for sensing both the passage of each carriage and the markings on an encoder strip on each transporter unit and a counter for counting same. It will be understood that the count kept by the counter represents the position of the designated transport unit relative to the fixed datum position to an accuracy of the spacing between the markings on the encoder strip and that from this the position of every other transport unit can be determined.
Whilst the central control system is able to determine accurately the instantaneous position of each transport unit relative to the fixed datum position from the count kept, this instantaneous position is only known to the on-board local controller or controllers on the continuous train when data is communicated to it/them by the central control system. Where data communication between the central control system and on the on-board local controller or controllers is two way data communication to the local controller or controllers will be interrupted due to the inherent delay in switching a transceiver from transmit mode to receive mode. Any inaccuracy in the position of the transport units as determined by the on-board local controller or controllers will, of course, result in it discharging its cargo in the wrong place.
To overcome this problem, the sortation system further comprises means for calculating the velocity of the continuous train and for conveying this information to the or each on-board local controller, together with the current positional data determined by the said distance determining means and the on-board local controller comprises means for extrapolating from the velocity of the continuous train the distance travelled at any instant between receiving the current positional data and new positional data being received.
Alternatively, two way communication between the central control system and the or each on-board local controller may be conducted on two separate channels. Data communication from the central control system to the on-board local controllers may take place on one of the said channels, whilst data communications from each of the on-board local controllers to the central control system takes place on the other channel.
Each transport unit is provided with an electric motor which is operable to cause the tray or belt associated therewith to operate. Power may be supplied to each motor separately, or through a common single supply unit, in which case the transport units must be linked together electrically as well as mechanically. Any one of several techniques may be employed to supply power to the electric motors, including:
1. a) A continuous electrical power source is positioned around the perimeter of the sorter track system and power is taken from this via a set of power pick-ups mounted on one or each transport unit, and used where needed.
b) A staged electrical power source is positioned adjacent to a short length of track enabling a power storage device on board one or each transport units, to pick up and store enough energy to facilitate a tip.
2. A rechargeable battery is provided on one or each transport unit. The rechargeable battery is recharged whenever convenient in the operating schedule of the system.
3. a) Electric power is transmitted to one or each transport unit via a method of magnetic induction. In such a method an electric current is induced from an inductive rail into a pick up carried on one or each transport unit, enabling the power to be used to tip a tray or operate a cross belt The inductive rail may be incorporated within the track or may be spaced therefrom. Where appropriate the transport units may be provided with a power storage device in the form of a battery or capacitor.
b) A staged inductive power transmission method can also be adopted. This will use magnetic induction to transmit power to one or each transport unit at locally selected xe2x80x98charging stationsxe2x80x99, after which the power is stored by a power storage device such as a battery or a capacitor.
4. Power can be generated on each transport unit by the use of a dynamo driven by the wheels of that unit. This may dynamically generate power to operate the discharge mechanism of the transport unit, or the power may be stored in a storage device such as a battery or capacitor for use when needed.
The transport units themselves can be propelled around the track by any of a number of conventional drive techniques, including friction wheel drive, individual motor driven carriages, belt drive, gripper drive, linear induction motor (L.I.M.), servo L.I.M., CAT/Chain drive, and screw drive.
By providing wireless communication between the central control system and each transport unit the performance of the sortation system over conventional systems is improved in several respects. To begin with wireless communication ensures that each transport unit is in virtually constant communication with the central control system. This means that any required command can be immediately relayed to the transport unit and acted upon. It also means that any change in the operating status of a transport unit can be immediately relayed to the central control system, and appropriate action can be instigated. Moreover, and perhaps most significantly, it means that the sortation system is no longer reliant on the positioning of each transport unit to achieve communication to and from the central control system.